RAPTOR RESEARCH

Rdptor Research Foundation, Inc.
Provo, Utah, U.S.A,

RAPTOR RESEARCH

Volume 14, Number 4, Pages 97-128
CONTENTS

Winter 1980

SCIENTIFIC PAPERS

Observations on Gyrfalcons {Falco rusticolus) Breeding

Near Lake Myvatn, Iceland, 1967-

Nick Woodin 97

THESIS ABSTRACTS 125

BOOK REVIEWS 127

RAPTOR RESEARCH

Published Quarterly by the Raptor Research Foundation, Inc.

Editor Dr. Clayton M. White, Dept, of Zoology, 161 WIDE, Brigham Young
University, Provo, Utah 84602

Editorial Assistant Elise V. Schmidt, 136 WIDE, Brigham Young University,
Provo, Utah 84602

Editorial Staff Dr. Frederick N. Hamerstrom, Jr. (Principal Referee)

Dr. Byron E. Harrell (Editor of Special Publications)

The Raptor Research Foundation, Inc., welcomes original articles and short
notes concerning both diurnal and nocturnal birds of prey. Send all papers and
notes for publication and all books for review to the Editor. Most longer articles
(20 or more typeset pages) will be considered for publication in Raptor Re-
search Reports, a special series for lengthy and significant contributions contain-
ing new knowledge about birds or new interpretations of existing knowledge
(e.g., review articles). However, authors who pay page costs (currently $36.00
per page) will expedite publication of their papers, including lengthy articles,
by ensuring their inclusion in the earliest possible issue of Raptor Research.
Such papers will be in addition to the usual, planned size of Raptor Research
whenever feasible.

SUGGESTIONS TO GONTRIBUTORS: Submit all manuscripts in duplicate,
typewritten, double spaced (all parts), on one side of 8 Vi X 11 inch paper, with
at least 1 inch margins all around. Drawings should be done in India ink and
lettered by lettering guide or the equivalent, if possible. Photographs should be
on glossy paper. Avoid footnotes. Provide an abstract for all papers more than
four double-spaced typed pages in length, not to exceed 5 percent of the total
length of the paper. Keep tables at a minimum, and do not duplicate material
in either the text or graphs. For advice concerning format refer to the Council
of Biological Editors’ Style Manual for Biological Journals or to previous issues
of Raptor Research, Proofs will be sent to senior authors only. Major changes in
proofs will be charged to the authors. Reprints should be ordered when proofs
are returned.

1981 MEMBERSHIP: (If paid prior to 15 February of each year)

$11— U.S. student

$13— U.S. regular and foreign student
$13 and $15 after 15 February.

OBSERVATIONS ON GYRFALCONS {FALCO RVSTICOLUS) BREEDING
NEAR LAKE MYVATN, ICELAND, 1967

by

Nick Woodin
Star Route

Ausable Forks, New York 12912

Introduction

This paper is based on observations made between 2 March and 23 August 1967 in the Lake Myvatn region
of northeastern Iceland and during a brief stay (24 to 28 August) on the island of Hrisey in the Eyjaf]ordur of
north central Iceland. I was supported during my stay in Iceland by a Fulbright Fellowship.

Iceland is one of the few places in the world where it is possible to study relatively abundant Gyrfalcon
populations from accessible and permanent human habitations. One of the reasons I have written up a single
season’s work at such length is in the hope that some other student will take up the study where I left it.

For advice and assistance I am indebted to Finnur Gudmundsson and Arnthor Gardarsson. Dr. Gudmunds-
son suggested the project, and without his and Arnthor’s help, it would have come to much less. I am grateful
to the staff of the Museum of Natural History, Reykjavik, for their kindness to a foreigner, and to Professor
Tom Gade for inspiration and advice.

The Region

Lake Myvatn is located at approximately 65V2° north latitude in the northern part of the arid, young-vol-
canic zone of Iceland. The lake, 277 m above sea level, is about 55 km inland from the north coast. Character-
istics of the young-volcanic zone are relatively low precipitation and much dry moorland, with a vegetation
chiefly of low-growing heaths (Ericaceae), creeping willows (Salicaceae), dwarf birch (Betula nana), and crow-
berries (Empetrum nigrum agg.) (Gudmundsson 1960). The Myvatn basin also contains extensive brushwoods
of birch (Betula pubescens) and large wastes of poorly vegetated sand, gravel, or lava. South of the lake lie
marshes with clumps of willow, The lake environs are excellent habitat for waterfowl. Bengtson (1971) esti-
mates that between May and September the area contains rarely fewer than 25,000 ducks. Shorebirds, includ-
ing Redshank (Tringa totanus). Golden Plover (Charadrius apricarius), Snipe (Gallinago gallinago). Dunlin (Ca-
lidri.^ alpina), and Whimbrel (Numenius phaeopus), also breed about the lake. There is at least one colony of
the Blackheaded Gull (Larus ridibundus). The region is the center of the distribution of the Icelandic Rock
Ptarmigan (Lagopus mutus islandorum), the only gallinaceous bird in Iceland (Gudmundsson 1960). All these
birds are potential prey for Gyrfalcons. Mammals are not common but include the Arctic fox (Alopex la-
gopus), long-tailed field mouse (Apodemitis sylvaticus), probably the mink (Mustela vison), and the brown rat
(Rattus norvegicus).

Lake Myvatn lies in a basin more or less enclosed by slopes, low hills, and mountains. What I have called
the Myvatn eyries are located in the canyons or on the exposed faces of the nearer hills and slopes (fig. 1).
They tend to be within 10 km of the lake and 100 to 200 m above it. By way of contrast, the highest moun-
tains near the lake range from 500 to 900 m above it, at distances of 12 to 15 km. The most geologically
isolated eyrie is Falkaklettur, which is located beyond the eastern hills on a high rock in the middle of an
extensive, well-vegetated lava field.

The farmers of the Myvatn basin raise sheep and cattle. Livestock graze outside for part of the year. Hay is
raised for winter feed, for the most part within a few hundred meters of the lakeshore. Sheep have exerted an
enormous influence on the Icelandic landscape, but other than that man’s effect on the wildlife of the Myvatn
basin has probably been relatively little. In 1967 farmers still supplemented their incomes by netting Arctic
char (Salvalinus alpina), and .shooting Rock Ptarmigan and Grey-lag Geese (Anser anser), but their harvests
were not excessive. The number of people in the basin is small. But as of this writing “modern life ” has
arrived at Lake Myvatn. The bottom mud of the northern, shallower basin of the lake is being mined to pro-
duce diatomaceous earth. This activity will force developnient of reliable year-round road communications
and a year-round port on the Greenland Sea. The lake is located within a geothermal area that is a potential
source of electric power. The next decades may well involve further industrial disturbances of the Myvatn
landscape, with unforeseeable effects on its wildlife populations, including its population of Gyrfalcons.

Purpose and Methods

I stayed with the family of Snaebjorn Petersson in Reynihlid (fig. 2). The chief purpose of my stay at My-
vatn was to determine whether the Gyrfalcons’ food habits showed any change over the breeding season. F.

97

Raptor Research 14(4):97-124

98 RAPTOR RESEARCH

Figure 1 Resident Gyrfalcon Pairs and Habitats at Lake Myvatn, 1967

Vol. 14 No. 4

Q

Birch Brushwood

S - ••

Bog/Swamp/Meadow —

Moorland

ED

Wasteland (unvegetated or

■ very sparsely vegetated)

El . •

Hills, Mountains

(Wasteland, unless otherwise noted)

A

A A

This map is intended solely
to give a general idea of the
, ' Lake Myvatn area. The

“habitat” categories are
Seliahjallagil O /\ catch-alls. In general the first
three habitats support breeding
populations of Rock Ptarmigan [Lagopus
. / > mutus) (though of greatly differing densities)
and also of the various species of shorebirds.
* ' The margins and islands of the lakes and

* . ponds, and the bog/swamp/meadow habitat

support the majority of the ducks, as well as
A the gulls and other waterbirds.

^ A
A

Gyduhnjuksgil

/\

A

Winter 1980

W oodin— Gy rfalcons

99

Figure 2 Eyrie Areas of Gyrfalcons at Lake Myvatn

O Gaesadalur

Seljahjallagil

Figure 2 summarizes my interpretation of eyrie areas at Myvatn.
Occupied areas are marked by a circle, former ones by a cross.
Alternate areas are joined by a solid line. Areas which I suspect
function primarily as alternate areas, but which are more than 3
km away from each other, are joined by a dotted line.

O Gyduhnjuksgil

100

RAPTOR RESEARCH

Vol. 14 No. 4

Gudmundsson and A. Gardarsson had observed that Gyrfalcon predation on the Rock Ptarmigan on Hrisey
virtually ceased the first week in June. They wanted to know if a similar shift away from ptarmigan as food
occurred at the eyrie. At the same time I was to fit in whatever other observations on Gyrfalcons I could.

Transportation was by ski, foot, and bicycle. Use of the bicycle became possible in mid-May. Until then I
observed the closest of the eyries: Seljadalur, Dimmuborgir, and Dalfjall (fig. 2). Seljadalur was just a 45-min.
ski from the house. When the Seljadalur pair failed to lay eggs, I focused on Dimmuborgir, with periodic
visits to the other eyries. A. Gardarsson had shown me the locations of most of the eyries before I left
Reykjavik.

One of my chief concerns was the extent to which my presence might influence the Gyrfalcons’ behavior.
Their reaction to me varied as the season progressed. They became more aggressive after egg-hatching. Be-
fore egg-laying, adults were rather shy, and it was difficult to assess one’s effect. I tried to remain as incon-
spicuous as possible. My equipment included 10 by 40 binoculars and a 30-power telescope. I did not use a
blind. The positions from which I watched the eyries were not always good. Rarely could I command a view
of both the eyrie and the approaches to it. At Seljadalur I generally picked a spot on the canyon floor, 250 m
or more from the nearest perching place. This position afforded a restricted horizon but a good view of the
interior of the canyon. A few times I observed from one of the ridges that bordered the canyon, where I had
an excellent long view in all directions but was unable to see most of the perching places in the canyon itself.

When I began regular observations at Dimmuborgir, the pair would tolerate me within 250-300 m as long
as I remained down near the valley floor. When I took a more commanding position on a slope, about 300 m
from the nest ledge, they began periodic fly-overs or otherwise indicated their agitation. I finally adopted a
position on the valley floor about 250 m from the nest ledge, which gave me a good view of the nest and of
the surroundings for a few hundred meters in each direction. My concern was to tell the direction from which
the mates were arriving, but this was rarely possible.

At Seljahjallagil I took a position that let me view the nest ledge, the inner walls of the canyon, and the
sandy waste and distant lake beyond. Thus I was able to observe in some cases the direction of arrival of the
adults with prey.

Falkaklettur was probably the best eyrie to observe. It was situated on a lava rock in the middle of a fairly
flat lava field. I could keep both the rock and approaches to it in view. After egg-hatching, however, the
female at Falkaklettur would not tolerate me within 500 m of the nest unless I remained completely hidden.

Early in the season I went out whenever weather allowed, generally for short periods of 4 to 5 hours. In
May and June my observations focused on Dimmuborgir, and I spent 4 to 8 hours a day watching the eyrie 4
or 5 days a week. In July and August I alternated longer trips to the distant eyries with shorter trips nearer
home. Long trips involved 2 to 3 hours of travel to the eyrie, 4 to 8 hours of observation there and a similar
amount of travel back. I spent about 700 hours in the field, 250 to 300 of them in direct observation of
Gyrfalcons.

The Eyries

Brown and Amadon (1968) define home range and nesting territory as they apply to diurnal raptors. The
home range is the entire area used by a breeding pair or solitary individual. The nesting territory is the area
about the nest that is defended. In some cases the two coincide, but often the “outer” parts of the home
range (which usually comprise the hunting territories) are not vigorously defended and may even be shared.
Cade (I960) uses a model of the latter sort to describe the home ranges of the Peregrine (Falco peregrinus)
along Alaskan rivers. His diagram of a typical home range consists of three concentric circles of increasing
diameter centered on the eyrie. The inner circle is always defended against other Peregrines. Inside the sec-
ond circle intruders are sometimes attacked, and in the outer circle other Peregrines are attacked only over
food items or favorite perches. The diameter of the inner circle varies from 100 m to 1.6 km, and that of the
outer circle is a little more than 3.2 km. The outer circles of adjoining home ranges overlap. The notion of a
large home range, vigorously defended for a small radius about the nest ledge, and loosely defended or even
“shared” at greater distances from the nest, fits my observations of Gyrfalcon behavior at Myvatn.

Beebe (1960) uses the term eyrie area to refer to the entire area in which, year after year, different nest
ledges are occupied by one pair of Peregrines. Gyrfalcons, like Peregrines, tend to use alternate nest ledges on
a given cliff or in a given canyon (Hagen 1952). However, at Myvatn two of the home ranges contained two
distinct eyrie areas, about 3 km apart, which appeared to function as alternate areas for the same pair. In this
case, it seems that the space between the.se areas .should not be classified with them. Rather one might refer
to them as alternate eyrie areas. At Dalfjall, on the other hand, several nest ledges were scattered along ap-
proximately 3 km of a mountain fault.

1. Dimmuborgir. The eyrie in 1967 was in an old nest of the Common Raven {Corvus corax) on a ledge in a
lava butte. The ledge faced west and was completely overhung. One could walk up to it. Another nest report-

Winter 1980

W oodin— Gy rfalcons

101

edly exists in Dimmuborgir, but I did not search for it. Dimmuborgir (Dusky Castles) is a lava depression,
roughly circular, between 1 and 2 km in diameter. A small central plateau is surrounded by a confusing maze
of lava buttes, pinnacles, and valleys. A pair each of ravens and Merlins {Falco columbarius) nested near the
part of the depression occupied by the Gyrfalcon.

The pair hatched 4 young from 4 eggs. Three of the young disappeared within a week, probably because of
my, or others’, interference. The fourth young died of unknown causes when virtually fully fledged. Dimmu-
borgir is a national park. One can drive to it, and after the first of June human disturbance is common. Be-
cause of its accessibility, it was also the eyrie I watched most frequently in May and June.

2. Dalflall. The eyrie area at Dalfjall consists of approximately 3 km of a fault that cuts through a moun-
tain ridge. Several inaccessible rocks and faces showed apparent Gyrfalcon use. The large cliffs overlooking
the plain to the east showed much use, held at least one former nest ledge, and seemed to be the center of
activity for the nonbreeding pair in 1967. Tbe previous year’s nest had been an old raven nest further north
along the fault. This nest was in a low face in a pothole just large enough to hold it. About 1 m below the nest
was a grassy ledge to which one could walk. A pair of ravens nested on the northern extremity of the fault in
1967. Gopulation and one attempted food transfer were observed in tbe Gyrfalcons.

3. Seljadalur. Tbe eyrie area centers on the east cliffs of a narrow canyon which opens out into a little
plain below. The cliffs are about midway along the canyon, where it narrows before bending abruptly 90°
and ending in a steep slope. The Gyrfalcons used several ledges and rocks on the western side of the canyon
in late winter and early spring, including an outcrop below the canyon proper. The only site that seemed to
show signs of previous nesting was an old raven nest on the east cliff. In April a pair of ravens began building
a new nest near the old one. After egg-laying by the ravens, a series of spectacular fights occurred between
the ravens and the Gyrfalcons, which finally resulted in the ravens remaining where they were and the Gyr-
falcons establi.shing control over a section of the cliffs with what appeared to be a .suitable nest ledge above
and up the canyon from the ravens. However, the Gyrfalcons did not lay eggs. Their ledge had fresh prey
pluckings and molted Gyrfalcon feathers on 20 July.

Whether the Seljadalur area is a separate eyrie area, or an alternate one (to either Dalfjall or Gaesadular,
most likely the latter) is not clear. Three factors make me question its separateness; it is rather close (about
5.5 km) to both Gaesadalur and Dalfjall; it is between Gaesadalur and Lake Myvatn; and vegetative signs
seem to indicate that Gaesadalur and Dalfjall have been more consistently occupied.

4. Vindbelgjarfjall The eyrie area centers on cliffs along the southeast side of “Windbag Mountain,” a
steep hill rising about 250 m from a marshy shrubland dotted with ponds. A pair of ravens nested in 1967 on
the western end of the cliffs and a pair of Merlins on the eastern end. At least one ledge in the central and
highest section .seemed to .show signs of former Gyrfalcon occupation, and this area also comprised the center
of activity for the nonnesting pair in 1967.

Breeding activity extended only through copulation. On 26 April 2 Gyrfalcons in juvenile plumage were
“escorted” away from the cliffs by the adults.

Between 4 and 5 km away over the moor is a low, rocky upjut that forms part of a bowl (Holkotsgil) in the
side of the Laxa River Valley. There I saw Gyrfalcons several times and found prey remains and molted feath-
ers. The upjut contains a raven nest, but as far as I could tell Holkotsgil has not l3een used by Gyrfalcons for
breeding. I think the Gyrfalcons I saw there were from Vindbelgjarfjall.

5. Falkaklettur. The eyrie area centers on a lava cone that rises about 6 m above a grassy base on the Bur-
fellshraun lava field. The Burfellshraun is well-vegetated and .supports breeding populations of ptarmigan and
shorebirds. The eyrie was in a north-facing hole, about 0.5 by 0.3 m, just below the top of the cone. A crevice
on the west face formed a narrow ledge through an accumulation of prey remains and pellets. It apparently
served only as a perch. A lava rock to the south showed signs of occupation by Merlins, but none nested there
in 1967.

About 3 km to the east is a group of upjuts (Kraeduborgir) with ledges that showed use by Gyrfalcons.
According to local farmers, this is an alternate site for Falkaklettur. 1 also found a site used by Gyrfalcons in
Threngsli, between 6 and 7 km .south of Falkaklettur. Here a small pothole or cave near the top of the cliff
had a mound of pellets, another of excrement (mutes), some old prey remains, and several recently molted
Gyrfalcon feathers. About 10 m around the cliff in a similar pocket was a new raven nest and about 15 m
further on an older one. The male at Falkaklettur was very shy of his mate, and possibly he used the first cave
as a perch. However, because of its distance from Falkaklettur it could have been a separate eyrie. If so, it
was not successfid in 1967. I found it on 7 August, 3 weeks after young fledged at Falkaklettur. As I climbed
about the cliff, 4 Merlins swooped and tumbled overhead.

6. Seliahjallagil. The eyrie area consists of the upper part of a narrow canyon (gil) that cuts into the upland
bordering the lake basin on the east. Two ledges showed use, but the only one I could identify as an eyrie was
that used in 1967. The slightly overhung ledge measured about 1 m by 0.3 m and was located on the south

102

RAPTOR RESEARCH

Vol. 14 No. 4

side of the canyon, with a grassy and stony slope below. It showed previous use. Four young were fledged in
1967. The lower part of the gil contained a volcanic crater, several of whose inner ledges showed signs of use
by Merlins. One held an eyrie, where 3 young were fledged.

Approximately 3 km south of the Gyrfalcon eyrie are two smaller canyons that open together into the plain
toward the lake, and immediately south of them are two bowls in the side of the upland, which has here
become a mountain (Blafjall). The more southerly canyon had a possible former eyrie site, and tbe northern
hollow at least two. The further hollow had one very suspiciously green ledge. Because of the area’s closeness
to Seljahjallagil I thought it an alternate area. An old raven nest in the southern part of Threngslaborgir could
also serve as an alternate site. Threngslaborgir is very confusing, and I could not find the raven nest again, but
it was also about 3 km from the eyrie at Seljahjallagil.

7. Qaesadalur. I found Gaesadalur on 17 August. The eyrie was on one of the ledges on the south side of
the valley, near where it opens into the plain Randir. The ledge was about 8 m above the valley floor, in-
accessible without a rope, and was apparently a much-used site, judging from the amount of orange lichen,
the thickness of the moss on the cliff, and the vigor of the Salix herbacea on the slope below. Chunks of moss
had fallen off the face, out of which I picked ptarmigan bones dyed a dark red. Juvenile down on a lower
ledge and along the shore of the pond, where there were also three recently picked-over duck carcasses, in-
dicated a brood had fledged. This face was the only eyrie site I found in the canyon, but the upland between
Gaesadalur and Seljadalur contains many likely-looking places.

8. Gyduhnjuksgil. I visited Gyduhnjuksgil on 12 August. The gil opens out into a dry wash in a stony plain
that rises slowly between the two mountains at the southern end of the lake. The area that contained the
former eyrie sites was the lower 150 m of the gil. About 1 km up the gil I found a rock on the west side that
looked like a Merlin site. The Gyrfalcon eyrie was in a raven nest on a rock face that stood out into the gil
itself. The nest was inaccessible without rope. There was another raven nest on a ledge below. A face near
the entrance to the wash had two possible former eyrie ledges, overgrown with tall grass. Juvenile down on a
perch at the entrance to the gil and fresh prey remains below the nest indicated that a brood had fledged.

9. Hrossahorg. Hrossaborg is not a Myvatn eyrie. The eyrie area consists of a crater whose walls make a
natural shelter for the level ground inside: thus, perhaps, its name— the horses’ castle, The crater is located
just south of the road across the Burfellshraun, about 3 km from the Jokulsa-a-Fjollum River, and 17 km from
Falkaklettur. It has four main cliffs, all of them on the outside. On 19 June, I found nothing on the northeast
cliff, a pair of brooding ravens on the northwest cliff, a partly collapsed old raven nest high up on the south-
west cliff, and a pair of Gyrfalcons with 4 downy young in a raven nest on the southeast cliff. The nest was
tucked into one of a series of long, .slanting shelves, about 3.5 m above a gravel slope. It faced east and was
completely overhung.

On 19 June the nest contained 4 large downy young. However, several things bothered me about tbe
adults. During the 3 hours I watched the nest, the male brought prey once. The female took it, fed herself,
and did not feed the young. I saw this happen very few times during my stay at Myvatn. It might have been a
response to my presence. Second, the color of the female’s plumage was midway between that of an adult and
a year-old juvenile. I was not sure her feet were yellow. Finally, during my approach to the nest the male was
much more aggressive than the female. Perhaps the female was a young bird breeding for the first time.

Between 19 and 24 June a photographer set a blind about 50 m from the nest. I dismantled it when I
visited the eyrie on 24 June. On this date, 1 young had disappeared, 1 was apparently dying, and the other 2
were somewhat lethargic. Neither adult appeared during the hour I spent there. On 26 June the remaining 3
young were dead. Neither adult was present. Apparently the nest was abandoned because of the blind, and
the young then starved.

Behavior during the Breeding Season

Pre-laying. A central question in the study of wild Gyrfalcons has been whether they
winter on the breeding grounds. Platt (1976), working in the western Canadian Arctic,
found Gyrfalcons in the vicinity of their nests in January and Eebruary. Bengtson (un-
publ. ms.) reports Gyrfalcons about Lake Myvatn in December. Platt (1976) presents
data that suggest that, at least in the higher latitudes of North America, the adult males
may remain on the breeding grounds over the winter while the juveniles move south.
Platt found potential prey. Willow Ptarmigan {Lagopus lagopus), relatively abundant in
January and Eebruary. TTie major difficulty for predators at high latitudes is probably
the short length of day (3 hours in mid-January for Platt’s plot) during which to obtain

Winter 1980

W oodin— Gy rfalcons

103

prey. Casual observations near Reykjavik, southern Iceland, during the winter of
1966-1967 indicate that at least some of the juvenile Gyrfalcons remain on the island.
They seem to suffer a heavy late autumn and early winter mortality from starvation and
disease (probably aspergillosis). Platt (1976) suggests that juvenile Gyrfalcons, lacking
hunting skills, tend to pursue ground-dwelling prey, such as lemmings, and disperse to
areas where such prey is more abundant for their first winter. In fact, Gyrfalcons may
learn to hunt on essentially ground-dwelling prey. The juvenile Gyrfalcons I watched in
late August in northern Iceland were catching juvenile ptarmigan on the ground. The
young Gyrfalcons would attempt to grab the young ptarmigan while flying over them
and, if this maneuver failed, would land and pursue them on the ground. One often sees
juvenile Gyrfalcons at the Reykjavik city dump in the autumn, where they pursue
brown rats {Rattus norvegicus).

Whether Gyrfalcons spend the entire year on their home ranges depends on the avail-
ability of prey. The Rock Ptarmigan, which forms the chief prey of at least the inland
populations of Icelandic Gyrfalcons, spends the autumn and winter grouped in nomadic
flocks, which perform a limited seasonal migration. In the autumn after acquiring white
winter plumage, ptarmigan move from their breeding grounds to higher elevations
where snow has already fallen. They then follow the snow line as it moves down the
mountains. Thus, depending on the other prey species available to a given population of
Gyrfalcons, one might expect a general autumn dispersal of Gyrfalcons (perhaps still in
family groups) in pursuit of ptarmigan, followed by a return, perhaps of the adults only,
to the breeding grounds in December, when snow cover is more general and the ptarmi-
gan more spread out. The return would depend on suitable winter cover for ptarmigan
being available in the home ranges of the Gyrfalcons. Suitable winter cover for ptarmi-
gan in Iceland consists primarily of brushwoods of birch {Betula pubescens). Since Gyr-
falcons breed so early and presumably need some weeks of socialization prior to egg-
laying, it may be that one of the prerequisites of a home range is a certain amount of
birch brushwood.

In March, when I arrived at Myvatn, Gyrfalcons were paired. At Dimmuborgir the
nest was being used for a perch. On 10 March a cup had been scraped. Upon my ap-
proach this day, the single bird did not leave the area directly, but circled several times
around the lava butte containing the nest before disappearing.

Prior to egg-laying, all the falcons spent a good deal of time perching, singly or to-
gether, in the immediate vicinity of the former nest sites. They also roosted near old
nests at night. The Seljadalur pair had perches both in the immediate vicinity and scat-
tered about the general area. The more distant perches were within 1.5 km of the can-
yon, mostly to the west and south. In April, after copulation began, they perched to-
gether for hours in the afternoon and evening, copulating every hour or two, and going
from one perch to another. It was not clear if the birds at Dimmuborgir and Dalfjall
made use of such distant perches. Hunting at this time still appeared to be a solitary
activity.

Ptarmigan were common in March and the beginning of April both in the birch scrub
on Dalfjall and at Seljadalur. Judging by remains found then and later during the thaw,
they had been taken by the Gyrfalcons at both places. Thus it seems that the free or safe
area for prey about the eyrie, which some observers have reported (Dementiev I960),
does not exist prior to egg-laying.

On 4 April I first observed copulation (at Dimmuborgir). It was accompanied by sev-

104

RAPTOR RESEARCH

Vol. 14 No. 4

eral vocalizations. Since the calls I recorded agree well with the repertoire described by
Wrege and Cade (1977), and that summarized by Cramp and Simmons (1980) for the
various events in the breeding cycle, 1 will not enumerate them here. I have made my
classification of calls in this paper fit theirs.

On 4 April preening movements by the female and many soft calls immediately pre-
ceded mounting by the male. During copulation the female bowed her head almost to
the ground, while the male balanced on her back, slowly moving his wings. After cop-
ulation the male left the area and had not reappeared by the time I left, an hour and 45
min later. Such disappearances at Dimmuborgir seemed the rule only for the first few
days. They also occurred from time to time at Seljadalur, and there was some indication
that they were associated with hunting by the male. On 8 April copulation in Dimmu-
borgir was accompanied by a chittering call.

Copulation at Seljadalur sometimes, but not always, involved more elaborate pre-
copulatory behavior. The most elaborate of such behaviors that I observed occurred on
5 April and consisted mostly of preening movements. The mates faced each other about
8 m apart on a snow-covered slope. First one bird and then the other took the initiative
at preening. The movements included lifting and preening under the wings; bending the
head back while elevating the tail, as though to touch the beak to preen gland; scratch-
ing under the chin; and lowering the head while bobbing the tail. One of the last in the
sequence, done only by the female, was a bending of the tail sideways, while reaching
back under it with the head. Such preening episodes occupied 20 min, when the male
took off and mounted the female, as usual, from the wing. Billing was part of the cop-
ulatory behavior at Dimmuborgir but not at Seljadalur. I also observed mantling of the
mates to each other during an afternoon of perching and copulation when the mates
were perched facing each other, less than a meter apart.

Flight display did not seem highly developed among these Gyrfalcons. The bulk of
their courtship behavior consisted of perching near each other. However, normal flight
patterns seemed to become more elaborate, or were executed with more speed or grace
during courtship. I twice saw mutual gliding during courtship. At Seljadalur this behav-
ior followed copulation. The mates soared above the canyon and then descended in long
glides, so that they crossed and recrossed each other’s paths. One dove from a short dis-
tance at the other, which I think turned on its back to meet it, and finally one followed
the other in a long swoop (I heard a burst of calls at this point) that carried them out of
sight.

Later in the season, from time to time I saw one or both of the mates at Dimmuborgir
perform a flight display above the eyrie; the bird would either soar with the eyrie as a
center below it or glide at a lower altitude in a series of circles or arcs that took it back
and forth over an area of 200 to 300 m radius. Twice during the fourth week of in-
cubation at Dimmuborgir, I saw one of the mates (once the female, once the male) go
into a stoop in the eyrie area, once right before the eyrie ledge and once a little way off.
In both cases the stoop was associated with a flight display above the eyrie. Finally, on
11 April, I saw a single Gyrfalcon make a morning flight at Seljadalur. That morning I
had been watching the canyon since 0445. Sun first shone in at 0700. At 0800 a gyr
appeared on the wing, swooped down across the valley, then up and back and dis-
appeared from sight. In less than a minute, the falcon came around the face again, made
a feint down, falling and twisting, then swooped twice way up, sliding down the rising
air currents above the top of the canyon. Finally it came motionless into the wind, high

Winter 1980

Woodin— Gyrfalcons

105

up, and then disappeared in a long circle. A few minutes later 1 spotted a gyr perched
on a face. It preened until 0830, and was still perched in the sun when 1 left at 0900.

Of the 4 pairs of gyrs 1 was observing in April only one pair (Dimmuborgir) laid eggs.
1 observed copulation in 3 of the 4 and suspect it occurred in all 4 pairs. At Dimmubor-
gir, egg-laying essentially marked the end of copulation. Egg-laying ended between 18
and 19 April. 1 observed only two copulations after this, on 19 and 24 April. One oc-
curred after 1 had disturbed the brooding bird (the male), and the other seemed to be a
substitute for the male’s failure to bring food. The last copulation I observed at the
other eyries was at Seljadalur on 20 April. On this day the birds spent most of my obser-
vation period (1000 to 1900) perching side by side on different posts within 1-1.5 km of
the canyon. Copulation occurred twice (once in the canyon, once about a km away). All
the pairs seemed to use their eyrie areas as a home base at least into June.

E^-Laying and Incubation. Egg-laying occurred about the middle of April. As nearly
as 1 could judge from the development of young in other eyries, the Dimmuborgir pair
laid eggs near the middle of a two-week laying period for the region. Egg-laying thus
coincided with the arrival of cock ptarmigan on the breeding grounds and also (but 1
think less significantly) with the arrival of the first migrant waterfowl. At Dimmuborgir
egg-laying also marked the start of fairly regular food transfers from male to female. It
was not clear when food transferring began or whether it was regular before egg-laying.
An instance of food transferring occurred near Dimmuborgir on 8 April, and I observed
an apparently unsuccessful attempt at food transferring at Dalfjall on 20 March. If early
food transfers occur on the hunting grounds, I would not have been likely to see them.

It was not clear whether the incubating female got all her food from the male or
whether she also hunted. Platt (1975) states that female Gyrfalcons do not hunt from the
beginning of food transferring through one week after hatching. The male at Dimmu-
borgir not infrequently appeared at the eyrie without prey and took over the in-
cubation, whereupon the female left for periods of up to 4 hours. The length of her
absences suggests she was hunting. However, she may have been retrieving prey the
male had cached or just “relaxing.” For several weeks after hatching, the female ceased
any semblance of hunting, and the male then hunted for himself, her, and the young.

To give some flavor of the Gyrfalcons’ behavior at this time, I quote two entries from
my journal. Several explanations have been advanced to explain sexual size dimorphism
in Gyrfalcons and other raptors (see Snyder and Wiley 1976). Of the several ideas Cade
(1960) favors the notion that females are larger because of their need to dominate the
male during the breeding cycle. One presumed reason for such dominance is to protect
the young from predation by the male. However, it may be as crucial for her to be able
to force the male to feed her during part of the breeding cycle. Gyrfalcons are active
hunters and “jealous” of their prey. In a sense, and within limits, the female’s larger size
lets her “force” the male to feed her (Cade 1960). Storer’s explanation (1966) puts for-
ward the idea that the size difference allows the mates to exploit more efficiently differ-
ently sized species of prey. There is some evidence that this is the case among other
raptors, especially in winter, and size differences might have some advantage for a pop-
ulation of Gyrfalcons that had access to differently sized species of prey. At Myvatn this
advantage would likely appear during July and August. I prefer Cade’s explanation be-
cause of its generality and because it seems to explain much of my data.

The first egg at Dimmuborgir was probably laid between 11 and 12 April. About
1330 on 13 April the female flew in to perch sideways on the nest ledge. The position

106

RAPTOR RESEARCH

Vol. 14 No. 4

was somewhat unusual: her usual position was perching with her tail hanging over the
edge. About 5 min later the male flew by the ledge and away, evoking a squawk call
from the female. Nothing then happened for about 2 hours. The female remained
perched on the nest ledge, facing inward, sometimes looking over her shoulder into the
valley. At 1515 the male swooped up and landed on the nest ledge, to wailing calls,
probably from the female. Both birds bowed to each other and seemed to scrabble on
the floor of the ledge with their beaks. While this went on, I heard a medley of
squawks. The male then moved by the female into the nest cup, where he remained for
a few moments, bowed forward. Just before leaving he half-squatted and made a motion
as though muting, and then flew to a nearby ledge where he looked back over his shoul-
der toward the eyrie. The female remained motionless for 3 or 4 min, bowed toward the
nest, then walked to its near edge and perched on its inner slope, still partly bowed
over. The male left about 1530. The female remained where she was until he returned
at 1700. During the hour and a half she preened for a few minutes and once gave a low
trech almost inaudible to me, accompanied by a jerk of the head. She held the same half-
bowed position.

At 1700 the male swooped up in front of the eyrie and landed above it on the butte.
The female hesitated a moment, walked through the nest-cup, and flew to a nearby
butte, where she perched, still tending toward the horizontal. 1 heard no calls. She let go
with a tremendous mute, took off, circled once, and swooped up very swiftly to perch
beside the male. I heard wailing calls, and the male plucked at a partly eaten ptarmigan
carcass in his talons. The female took off again, circled, floated perhaps 6 m over the
top of the butte, then settled slowly beside the male. For 3 or 4 min there was much
chittering such as accompanied copulation. The female seemed to be pushing against the
male’s belly with her tail and flank. He finally moved away, and she started to pluck at
the carcass. Perched upright on a rock, he let her feed for about 7 min. Normally, feed-
ings last 20-30 min. Tben he approached her from the front and after a few false tries
picked up what was left of the carcass and flew away. The female remained for some
minutes, picking up a few bits, and then took off, gained height, circled once very fast
over the little valley, and swooped up to the nest ledge. After a few minutes she walked
to the nest and climbed over it to its inner edge, where she fluffed her feathers, spread
her wings, and settled down in the same half-bowed position she had been in before. She
remained so for the half hour until I left at 1800.

What one might note in connection with Cade’s hypothesis is the change from wail-
ing calls to copulative chittering which preceded the male’s release of his prey to the
female, as well as the moderation of her movements in her second approach to him, in
contrast both to her first approach and her return afterwards to the nest. She also al-
lowed him to remove the remains from her possession. While she appeared subservient,
I thought her behavior pattern implied dominance. She walked a narrow line between
frightening the male away and getting him to bring her food (I do not mean to imply
she was “conscious” of this).

By 28 April, incubation had been under way for about 10 days. At 1700 the male,
who had been absent from the vicinity of the eyrie for at least an hour and a half, reap-
peared on a perch near the eyrie. The female apparently did not see him approach: the
perch is not visible from the eyrie ledge. He had a full crop. After 1 hour and 45 min
the male swooped up in front of the eyrie ledge to land on top of the butte. As he
swooped by, I heard the wailing call. The female left the eggs and flew to a nearby

Winter 1980

W oodin— Gyrfalcons

107

butte and began repeating the call. She then flew back to the butte and landed right
beside the male; there was a slight scuffle in which she may have actually pushed him
from his perch, upon which he flew directly to the nest ledge, walked into the nest, and
began to incubate. The female settled down, feathers all fluffed out, as if to incubate, then
hopped back, perched, and began to preen. She preened steadily for about 20 min, res-
ted, then mantled and preened off and on for another 20 min, whereupon she flew.
About a half hour later the male left the nest without a sound; I then heard a wailing
call, and he swooped up as if to perch, out of my sight. I heard another wailing call
ending in duckings, and 2 or 3 min later the female flew around the eyrie butte,
swooped up to the ledge, and began again to incubate.

In the light of Cade’s hypothesis, I would interpret this sequence of behaviors as fol-
lows: the male made a “mistake” by landing without first showing himself to the in-
cubating female. Recognition between the Gyrfalcons seemed to be by sight; vocaliza-
tion was secondary. The male usually flew by the nest ledge or otherwise showed
himself when appearing in the vicinity of the nest. He had fed, which implied, if they
were sharing prey, that she was hungry. The female then acted as if she had expected
him to bring food; this accounts for the “scuffle.” But the male had not brought food.
The female’s preen and apparent “dust bath”— the sole time I saw such a performance
on the top of the butte— indicated her “anxiety” or “confusion” over his not having
brought prey. In this context her mantling was quite remarkable. It has been suggested
to me that she was “rousing,” but my journal records “mantling.” Finally she left the
area, perhaps to hunt, perhaps to obtain food from a cache, perhaps to exercise. Her
short absence makes it unlikely, though not impossible, that she was hunting. While one
can argue that the female’s behavior was a result of her being “tired” of incubating and
simply taking advantage of the male’s presence to preen and “relax,” this explanation
does not adequately account for the details of her behavior, while Cade’s notion does.

The female performed the main part of the incubation duty. She was not always re-
lieved by the male while she fed. At those times the eggs remained unattended for
20-30 min. Both sexes made many of the same movements while on the eggs. They con-
sisted of (1) an incomplete rotation, which involved a rocking from side to side of the
body, a back and forth shuffling of the feet, and later a downwards bumping of the belly
(these movements I assume were to accomplish a turning and regrouping of the eggs);
(2) a picking up and dropping of the material in the nest cup with the beak; (3) preen-
ing; (4) snapping at flies. The time between egg turnings was variable and ranged from
over an hour to a few minutes. The function of her handling of the nest cup material
with her beak, if not merely a nervous release, might have been to keep the nest mate-
rial, which tended to become compacted, broken up and soft and thus a better in-
sulation against the cold. I did not observe the male handling the nest material in this
way.

TTie mechanics of nest exchange ceremony varied greatly. The female’s departure (if
she was going to go) seemed to be stimulated simply by her awareness of the male’s
arrival in the vicinity. When she departed, the male would then either go or not go to
the eggs: I could not distinguish a pattern. If he did not begin to incubate, she returned
to the eggs, though sometimes with a delay of 20-30 min. Only occasionally did he in-
itiate the exchange of incubation duties; this he did by flying to the eyrie ledge and
calling gently until the female surrendered the eggs. His way of surrendering the eggs to
her was also variable. Sometimes the mere sight of the returning female was enough to

108

RAPTOR RESEARCH

Vol. 14 No. 4

make him depart. Other times he left the eggs only reluctantly and with much urging on
the part of the female. 1 did not discover an evolution of the ceremony over time: one of
the least ceremonious of the exchanges occurred on 18 May and one of the most reluc-
tant on 19 May (both near the end of the incubation period).

From about the second week of May onward (the last two weeks of incubation), the
male began to make more frequent and vocal visits to the eyrie. This behavior con-
trasted with his previous habit of alternating long periods in the nest area with long
periods of absence. Perhaps this change was a preparation for the more frequent feeding
visits after hatching. Sometimes the female left the eggs when he appeared but would
immediately return to them. The male’s visits were accompanied by much screaming
and clucking. They did not seem to be accompanied by an increase in the frequency
with which the male brought prey.

A summary of data for the incubation period at Dimmuborgir follows:

• 11-12 April, 1st eggs probably laid (13 April observation).

• 18 April, 1500, 3 eggs laid.

• 19 April, 1530, 4 eggs laid.

• 22 May, 1230, the young in at least one of the eggs squeaking. No chipping appar-
ent.

• 23 May, 1130, 2 eggs cracked near the large end, the 3rd had a small hole on one
side of the large end.

• 24 May, 1100, 2 dry young, 1 wet young, 4th egg cracked.

• 25 May, 0830, 4 dry young.

Incubation time for the fourth egg:

Maximum time— 18 April, 1500, to 25 May, 0830, or 36 days, 1714 hrs.

Minimum time— 19 April, 1530, to 24 May, 1100, or 34 days, 1914 hrs.

Thus the incubation period for this egg was 35-37 days. It is about a week longer
than the 28-29 days reported by Brown and Amadon (1968). It is similar to the 35-day
incubation period noted for captive Gyrfalcons by Cade and Weaver (1976). Platt
(1976) noted 35 days for incubation of wild Gyrfalcons without specifying details. My
estimate of the timing of the first egg depends on Platt’s observation of 8 days for laying.

Aggressiveness toward Man, At Dimmuborgir, eyrie defense showed a definite in-
crease up to hatching, leveled off for a few weeks, and then fell. As the time of hatching
neared, the brooding female sat tighter upon my approach. Finally she let me come
within about 3 m before flying and would return immediately after I left the ledge. On
23 May the pair screamed at me while I was at the nest, and on 25 May one or both
stooped at me for the first time but did not come close. Thereafter their aggressiveness
toward me slowly declined. On 5 June the female still stooped; on 16 June she merely
flew back and forth above the eyrie screaming.

Females at Seljahjallagil and Falkaklettur were much more aggressive. The Falkaklet-
tur female once struck me, and the Seljahjallagil female would dive repeatedly within
less than 1 m of me. The aggressiveness of the female at Falkaklettur increased as in-
cubation progressed and did not decrease after hatching. She sat much tighter than the
Dimmuborgir female. Her aggressiveness seemed to be focused either on defense of the
rock or (more probably) of prey, rather than on defense of the young. On 11 July, less
than a week before the young left the vicinity of the eyrie, she dove repeatedly at me
when I climbed the rock to collect prey remains, even though the young remained in
the lava field below. She then ignored me when I tried to catch the young to weigh

Winter 1980

W oodin-Gyrfalcons

109

them. The female at Selljahjallagil behaved similarly. On 19 July she attacked me while
1 was on the slope below the nest, something she had never done before. At this time,
however, the slope, rather than the nest ledge, was the place to which prey was
brought. At any time, the presence of more than one person made the attacks of both
females less aggressive and, if I happened to arrive when they were away, the attacks
upon their return seemed less vigorous.

In descending order, the aggressiveness toward me of the breeding females 1 was ob-
serving was: Falkaklettur, Seljahjallagil, Dimmuborgir, and Hrossaborg. The eyries with
the more aggressive females were also more successful in fledging young. This observa-
tion could be interpreted as supporting the case for a relationship between female do-
minance and success in fledging young. One must assume that the aggressiveness of fe-
males toward a human intruder was a measure of their tendency to dominate their
mates as well. It is also clear that too much female aggressiveness will create an impos-
sible breeding situation: what is required is the proper aggressive balance for a pair.
Although the females that were the most aggressive toward me were also the most suc-
cessful in raising young, the second most aggressive female raised what appeared to be
the most healthy and vigorous young. The male of that pair was also considerably more
aggressive toward me than the males at other eyries. The Falkaklettur male seemed to
visit the nest very infrequently and cautiously, which may have been a sign of his fear of
the female. The whole issue of success in fledging young becomes confusing because of
the different locations of the nests, the implied differences in prey available, and the
differences in the hunting abilities of males. These factors may also be related to aggres-
siveness, but not solely to it.

Nestling, Period. Most of my information concerning the nestling period comes from
the Dimmuborgir eyrie.

After hatching, the male did all the hunting. Brooding by the male was rare. Twice I
saw him begin to brood the young while the female left to carry off prey remains. Jen-
kins (1974) reports brooding of the young by the male while the female fed.

I saw only the female feed the young. She always took some of the prey for herself,
and on at least one occasion (27 May), she fed herself from a carcass before bringing it
to the chicks. Usually she fed herself and the young concurrently, concentrating first on
the young, then for a while on herself, then on the young again. Such feedings usually
took 20 to 30 min. Wayre and Jolly (1958) report feeding times at a Myvatn eyrie of
about 16 min and state that feeding by the male was not uncommon. After feeding, the
remains of the prey were sometimes removed, usually in the feet. Twice the female left
carrying such remains in her beak. Because of this removal I could not calculate the
total amount fed. I could not discern a regular daily pattern in feeding. Some days had
many and other days few feedings.

The ceremony surrounding the exchange of prey between male and female had be-
come quite regular by the time of hatching. In the first weeks after hatching, while the
female was remaining near the young or in the immediate vicinity of the eyrie, prey
exchange occurred near the eyrie, as it had during incubation. A relative innovation was
the commencement of wailing calls by the female after receiving prey, or after arrival
of the male without prey. Sometimes she stopped such calls by herself and sometimes
only after the departure of the male, who during incubation often stayed in the area for
an hour or so after bringing prey. In the most remarkable instance (in this case he had
brought in prey) she called continuously for 16 min until he left the area. Jenkins (1974)

no

RAPTOR RESEARCH

Vol. 14 No. 4

reports the caching of uneaten remains about the nesting cliff. This I did not observe.

During the first week after hatching, the female spent most of her time brooding,
leaving the nest for only short periods. By the second week, the single remaining young
had grown sufficiently to move about the nest and disturb the brooding female. She still
spent most of her time brooding, leaving only for short periods. During the second week
I heard the young calling during feeding periods. Begging consisted of shaking the raised
head stiffly back and forth and calling.

By the middle of the third week the chick at Dimmuborgir was too big to brood com-
fortably, but the female still spent most of her time standing over or near it. Brooding at
Falkaklettur stopped during the third week. This eyrie had three young, however, and
brooding probably became physically impossible as well as unnecessary earlier. Wayre
and Jolly (1958) report that brooding was over by the fourth week, but that the female
remained almost constantly in the vicinity of the eyrie. During the third week at Dim-
muborgir the young began to take a more active part in the feeding process and often,
when the female held a bit of food before it, would move to take the food from her
beak.

By the middle of the fourth week the young at Falkaklettur were flapping their
wings. Wayre and Jolly (1958) report the same observation. At Dimmuborgir, from my
observation post, quills became visible through the down during the fourth week, and
the chick also began preening and flapping its wings. Cade (1960) assumed young gyrs
are 3 weeks old when quills showed. The young now moved vigorously about the nest
and called. The female was still spending most of her time in the nest near the young
but would leave the nest for periods of more than an hour.

During the fifth week the Dimmuborgir female abandoned her position in the nest for
one on the eyrie ledge, and by the end of the fifth week she abandoned the ledge but
still remained in the area. Her wailings calls were becoming hoarser, more like those of
early March. On 27 June (nestling about 33 days old), she left the eyrie area for an hour
and a half.

During the fifth week the chick bent toward the prey as the female fed herself. Every
now and then it managed to steal a few bits from the carcass or from her beak. On 27
June it moved to the edge of the ledge to mute. The mute shot clear of the ledge. Jen-
kins (1974) connects this practice and the removal of prey remains with the need for
nest sanitation— to minimize infection of young by parasites or disease. But removal of
prey remains seems to be practiced irregularly. Bengtson (1971) reports “heaps of re-
mains” under some nests. I saw a similar condition at Gyduhnjuksgil, where rotting re-
mains were scattered on ledges all over the cliff. It may be that as long as the remains
are off the nest shelf the dangers of parasite buildup are minimized; such removal tends
to occur naturally with older young, who knock them off. Furthermore, adults presum-
ably suffer some risk to themselves in trying to remove remains from under the feet of
well-grown young. The removal of remains by the adults might then be restricted to the
early weeks of the nestling period. The accumulations found under nests would occur in
later weeks. Removal of remains from the eyrie area by the gyrs early in the nestling
period would tend to bias late-season prey collections against prey taken preferentially
early in the season.

During the sixth week the Dimmuborgir young began to feed itself, and the female
apparently began to hunt again.

If the Dimmuborgir female began to hunt between 27 June and 2 July, she began

Winter 1980

Woodin— Gyrfalcons

111

comparatively early. The gyrs at Falkaklettur and Seljahjallagil bred slightly earlier. At
Seljahjallagil, the female could have been hunting on both 13 and 19 July and almost
certainly was by the 25th. I do not think the female at Falkaklettur was hunting on 11
July, though I assume she had begun by 13 July, when the eyrie was deserted. Thus,
allowing for the difference in the breeding cycle, the females in the last two eyries
started hunting between 3 and 4 weeks. Cade (1960) states that in the latter days of the
nestling period both the male and female hunt; Wayre and Jolly (1958) found a Myvatn
female hunting during the fourth week of the nestling period.

Fledgling Period. Jenkins (1974) reports 45-47 days for fledging. On 9 July the 8-
week-old young at Falkaklettur were flying. On 12 July I found the 7-week-old young at
Dimmuborgir dead on the slope below the eyrie. It had been alive on 9 July, with the
female present. It was fully fledged and weighed 660 gm. The young at Seljahjallagil,
which were less than a week older, all weighed more than 1000 g on 13 July.

The Falkaklettur eyrie was empty when I visited it on 13 July but showed signs of
some further use (juvenile down, prey remains) when I visited it again on 7 August. The
adults brought food to the young at Seljahjallagil at least until 3 August (their 11th
week). I did not visit this eyrie again until 19 August (the 13th week), when it was
deserted except for a pair of scavenging ravens. Bringing the prey to a central feeding
place (first the eyrie ledge, then the slope below) ceased between 19 and 21 July. From
21 July on, remains were scattered all over the canyon. Cade (1960) mentions a brood of
young gyrs that were flying on 10 July and still near the eyrie the second week of Au-
gust. Bengtson (1971) states that Cyrfalcon eyries at Myvatn are “abandoned” the last
week in June or first week in July.

I first saw young Cyrfalcons near the lake on 28 July (the 10th or 11th week for juve-
niles) and after that found signs of them along the east shore. I did not see adults in their
company, but I had them under observation too briefly and too infrequently to know if
they were still being fed by adults. Eyries at Caesadalur and Cyduhnjuksgil, which had
both raised young, were deserted when I found them on 17 and 12 August, respectively
(the 12th or 13th week for the other broods).

Generally, then, it seems that within 2 or 3 weeks of learning to fly the young start to
follow their parents to the hunting grounds. At this time these grounds are the shores of
the lake, which from mid-July to mid-August are home for thousands of young and vul-
nerable ducks, shorebirds, and gulls. The eyrie areas are now either abandoned or used
only sporadically. Platt (1976) reports observations by Wiseley and Rosier of apparent
“family groups” of juvenile Gyrfalcons still together on the “hunting grounds” in Sep-
tember. Whether the young were still being fed by the adults was not clear.

Adults appeared to cease feeding young toward the end of August. I spent 24-27 Au-
gust on Hrisey, an island off northern Iceland with a large breeding population of Rock
Ptarmigan. This would be the 14th week for the Myvatn juveniles. At this time, two
juvenile Gyrfalcons were apparently successfully feeding themselves on juvenile ptarmi-
gan that they caught on the ground. The presence of the young gyrs on this island in the
middle of the fjord, 4 km from the mainland and probably at least twice that from their
eyrie, strongly suggests that the young followed the adults there.

The productivity of 1967 is shown in table 1.

112

RAPTOR RESEARCH

Vol. 14 No. 4

Table 1. Productivity of Gyrfalcon Eyries near Myvatn in 1967.

Eyrie Eggs Eggs hatched One week 4-5 wks Fledged & flying

Dimmuborgir 4 4

Falkaklettur 4 ?

Seljadalur 0

Seljahjallagil ? ?

Dalfjall 0

Vindbelgjarf]all 0

Gaesadaliir ? ?

Gyduhnjuksgil ? ?

Hrossaborg ? ?

4 1 0

? 3 3

? 4 4

? ? ?“

? ? ?“

? 3 O'

"Unknown number of young raised to flying age in each case.

‘Four young were present on 19 June, three on 24 June (when the wing quills were poking through). All were dead in the nest on 26 June. The
cause of death was probably starvation. Between 19 and 24 June a photographer set up a blind about 50 m from the nest; I dismantled the blind on
24 June. By then one young was apparently dying, and the other two were quite lethargic. Neither adult appeared during the hour we spent there.
The three dead young are presently in the collection of the Museum of N atural History, Reykjavik.

Agonistic Behavior

Interspecific. Three predatory birds— the Common Raven, the Gyrfalcon, and the
Merlin— are regular summer residents of the Lake Myvatn basin. The raven and Gyrfal-
con remain in the region for much of the year; the Merlin is migratory. Except for a
small over-wintering population of ducks— primarily Barrow’s Goldeneye {Bucephala is-
landica), Goosanders (Mergus merganser), and Mallards {Anas platyrhynchos)— the only
prey available to Gyrfalcons during the winter and early spring is ptarmigan. Ravens are
both predators and scavengers. They probably scavenge prey remains left by the gyrs,
but the importance of such remains in their diet is unknown. Judging from signs about
the remains, the ravens, at least in winter, face considerable competition for them from
Arctic foxes.

The three predators often nest near each other. The situation in 1967 is detailed in
the eyrie description under The Eyries. I did not make an exhaustive search for raven or
Merlin nests, but nesting associations seemed to be the rule rather than the exception.
The only nests of either Merlins or ravens of which I was aware, other than those near
Gyrfalcon eyries, were two suspected eyries of Merlins. The frequent use of raven nests
by gyrs might help explain the gyr-raven association, but the Merlin-gyr association re-
mains something of a mystery. There does not seem to be a lack of suitable geological
structures for nest sites for any of these species in the Myvatn basin. However, various
writers have reported finding Gyrfalcons nesting near other raptors. Hagen (1952) re-
ports eyries of the Gyrfalcon and the Rough-legged Hawk {Buteo lagopus) within 60 m
of each other. White and Cade (1971) report nests of the Gyrfalcon and Peregrine with-
in 40 yds and those of the Gyrfalcon and raven within 20 yds. In no case did I find nests
closer than 200 m. White and Cade (1971) suggest ravens use Gyrfalcons’ cliffs in order
to scavenge the gyrs’ prey remains. I saw no scavenging near the nest cliff itself as long
as the Gyrfalcons were in residence.

1 saw two aggressive encounters between Merlins and gyrs. On 17 May in Dimmubor-
gir, the male gyr returned about a minute after leaving the eyrie with a Merlin stooping
at him but not touching him. After two or three stoops the Merlin departed. It did not
follow the gyr into the immediate vicinity of its eyrie. The gyr ignored the attack and
soared over the eyrie upon his return.

Winter 1980

W oodin— Gyrfalcons

113

The other incident occurred at Vindbelgjarfjall, where the Merlins were nesting and
the gyrs not. In this case, the male Merlin attacked one of the gyrs that flew in right
over its nest. The Merlin chased the gyr into the gyrs’ usual perching area, then dis-
lodged either it or another from a perch, and finally dove again and again at one while
the other circled nearby. Eventually the Merlin departed, and the gyrs returned to the
cliff. One of the gyrs was screaming at the beginning of the attack, but neither at-
tempted to attack the Merlin.

The one case of clearcut competition for nest sites occurred at Seljadalur. During
March and April a pair of ravens and a pair of gyrs shared the canyon in apparent
peace. The gyrs used the valley (mostly, however, the west cliffs which had not been
used for nesting by either species) for roosting and perching. The ravens started building
a nest on the east cliffs (the traditional nesting cliffs) about 1 April. As far as I could tell,
the gyrs did not pick a nest site, though I found some evidence of scraping on a ledge on
the west cliffs on 27 April. A nest here would have been right across the narrow canyon
from and in full view of the raven nest. A nest in the former gyr site (old raven nest)
would have been level with, in sight of, and perhaps 30 m from the new raven nest. The
ravens began to brood about 27 April. On 30 April, alerted by excited croakings from
the ravens, 1 saw a gyr (probably a male) make a feint at a raven perched on a ledge of
the east cliffs. It did not actually strike the raven, both birds flew up, the raven got
above the gyr and lunged down, and both birds fell almost to the valley floor, turning
round and round and apparently grappling. Then the gyr flew straight away screaming
with the raven in pursuit. A few minutes later the raven returned to the canyon.

On 8 May I arrived at 0500 at Seljadalur. As on 11 April, the ravens were then active.
The gyrs became active about 0800. The gyrs were roosting in the canyon, and a ledge
of the east cliff above and upvalley of the raven nest showed much new use by gyrs. The
ravens did not follow me to this area of the cliff. No interaction occurred this morning
though both species were present. I heard what sounded like a quarrel on 13 May, per-
haps stimulated by a low-flying airplane (a rare occurrence which usually brought the
gyrs into the valley). The gyrs continued to use that ledge at least into July.

Interspecific competition may have prevented the Gyrfalcons in Seljadalur from nest-
ing, but I doubt it. April 27 is at least a week later than any of the other Gyrfalcons in
the area began laying. Moreover, two other pairs of gyrs near the lake also failed to lay.
The Seljadalur gyrs were successful in establishing themselves on the east cliffs and
seemed content there. Although competition with the ravens provided yet another
stress, I suspect the primary stress causing nonbreeding at Myvatn in 1967 was a relative
lack of prey.

I saw one agonistic encounter between ravens and gyrs that was apparently over
hunting grounds. On 19 March I was coming across the lake on the ice toward a shrubby
hill where I frequently found either gyrs or ravens, when I saw a raven and a gyr above
the hill, each of them calling and circling. At first, the raven, who had the height advan-
tage, dived at the gyr, then it ceased diving but kept its advantage. The gyr eventually
broke off and flew down to perch on a rock, after which the raven descended, but did
not land. It was joined in the air by another raven. The ravens flew off together, and the
gyr remained perched.

During the summer, gyrs that hunted from perches along the lakeshore were struck at
by passing Arctic Terns {Sterna paradiseae). It seemed an almost casual display of antag-
onism. The Gyrfalcon would flinch but not fly, and the terns never seemed to gang up
to drive it away.

114

RAPTOR RESEARCH

Vol. 14 No. 4

Intraspecific. I observed no intraspecific quarrels over perching posts or hunting
grounds. In fact, there was some indication that, at least in March and April, hunting
grounds were shared by gyrs of different pairs. The only space I saw defended from
other gyrs was that immediately about the eyrie.

On 16 June the male returned to the Dimmuborgir eyrie from a 2-hour absence in an
unusual fashion— slowly circling, both gliding and flapping, toward the eyrie butte. Both
performing such a display upon his return and the form of the flight movements them-
selves were unusual. He was not high, passed over the eyrie and beyond, then returned.
The female saw him but did not respond. Suddenly she left the eyrie, and I saw a third
gyr flying overhead on a path that would take it right over the eyrie (toward Seljahjalla-
gil). Both gyrs were on the interloper immediately. First the female grappled at it from
below, and then the male dropped on it from less than a meter, so that it had to flip
over and present its talons upwards. It was attacked once more, then merely closely fol-
lowed, until they were 200-300 m south of the eyrie, when the pair broke off and re-
turned, gliding close together, then soared separately over the eyrie for about 10 min,
keeping within a radius of perhaps 250 m. At this time (2 weeks after hatching) the pair
was at the peak of their aggressiveness toward me. Earlier in the season the incubating
female had shown some reaction (once even leaving the nest) to Greylag Geese {Anser
anser) that passed directly overhead.

Finally, at Vindbelgjarfjall on 26 April I watched the adults chase away (perhaps, “es-
cort away”) two gyrs in juvenile plumage. I had been watching the cliff for 2 hours
when the adults appeared. One landed in view, and the second disappeared into a cut in
the cliffs and began to scream excitedly. At this point a juvenile flew from behind me,
heading toward the cliff, and the adult reappeared from the cut, followed by another
juvenile. The three gyrs on the wing flew screaming along the face, the other adult then
joined them, and all four flew out of sight around the mountain. An adult soon returned,
circled, and disappeared into the cut. The other adult appeared and perched on the
open face. In about 2 min the juveniles returned from the direction in which they had
gone, one flying straight for that invisible ledge in the cut. Both adults then gave chase,
sometimes dropping down toward a juvenile from just above it but for the most part just
staying near the young birds. Once a young bird flipped on its back as though to grapple
with an adult. An adult circled back and began to land, when a juvenile flew right over
its head, not making any move down toward it. The adult flinched, I heard screams, and
the two flew away along the cliff. I heard more screams after about a minute and saw a
gyr circling, but then all was quiet. A search of the part of the cut that had seemed so
intriguing revealed the fresh carcass of a ptarmigan on an inaccessible ledge.

This occasion was my only certain sighting of juveniles from the previous year at My-
vatn.

Sharing of Hunting Grounds

Several times in March and early April, up until cock ptarmigan began setting up
territories, I saw what were apparently Gyrfalcons from different eyries hunting the
birch scrub northwest of Dimmuborgir, at distances of from 2 to 5 km from the Dimmu-
borgir eyrie. Cade’s (1960) schematic of the breeding territories of Peregrines along the
Yukon River implies that the outer parts of the territories may be shared in this species.
Whether Gyrfalcons usually share, or do not defend, their home ranges, except for a
limited area about the eyrie, is unclear. The only territory I saw defended from other
gyrs was that immediately about the eyrie. I did see a Gyrfalcon drive a pair of ravens

Winter 1980 Woodin— Gyrfalcons 115

from what was a favorite hunting area for both species. The spot was 4 km from the
Dimmuborgir eyrie (the closest).

In late winter and early spring ptarmigan are virtually the only food available to the
Myvatn Gyrfalcons. Since at this time the ptarmigan feed heavily on birch catkins, birch
shrubland is the favored hunting ground for the gyrs. Such shrubland is limited in extent,
and the ptarmigan population of a given piece of it seems to fluctuate daily. Thus a
certain amount of pressure exists for sharing hunting areas. When about the middle of
April the cock ptarmigan set up territories and spread out over larger areas, this pres-
sure would appear to be reduced. Such pressure might rise again in late June, over areas
favored for the taking of ducks, gulls, or shorebirds.

Nest-Site Selection

Cade (1960) states that 18 of the 21 Gyrfalcon eyries he found along the Colville Riv-
er were overhung. He thought that the extensive use of old raven nests by gyrs in part
explains the overhangs. Ravens, like gyrs, nest before melt-off and choose an overhung
site for its protection from the snow.

To test this hypothesis I noted the snow cover on several overhung and non-overhung
former eyrie sites during March and April. The overhangs did not seem to make much
difference to snow cover. In fact, the high winds frequent to the area sometimes blew
the exposed ledges clear while drifting over the overhung sites. My chief non-overhung
site, an old raven nest in Seljadalur, did not seem to accumulate more than a few inches
of snow at any time.

Unfortunately these observations cannot be taken to mean that snow cover is not a
factor in nest-site selection by ravens and gyrs, nor that overhangs may not, in many
situations, prevent snow and ice from building up on a potential nest site. However,
especially among ravens, the choice of an overhung site may have to do with something
other than snow cover— concealment of the nest, for instance.

Hunting

On 4 March I watched Gyrfalcons attempt two kills. The first resembled the “tail
chase” described by Cade (1960), White and Weeden (1966), and Bengtson (1971). It
was snowing, and I had picked a spot to sit where I had seen ptarmigan the day before.
After I had been there about 15 min, a ptarmigan flushed, about 40 m away. Ten min
later a ptarmigan flew over my head with a Gyrfalcon about a meter and a half behind
it and gaining altitude. The ptarmigan dived into the scrub, whereupon the falcon
turned abruptly and plunged down into the scrub also. They were then about 60 m
away. Five min later the gyr reappeared from the same spot without prey. Later, I saw
a gyr flying over the scrub turn abruptly and dive down, seemingly to the ground.
Twenty sec later the gyr reappeared and flew away, whether with or without prey I
could not tell.

These incidents differed from what I saw when the ptarmigan were displaying in that
there is some suggestion that the Gyrfalcon sighted its prey while flying. In March I
occasionally saw gyrs flying low over the scrub. The ptarmigan along their flight path
either froze or flushed, in the latter case exposing themselves to pursuit. However, I
never saw a gyr strike in this situation. Similarly, ducks often flew rather than swam
away if they were too close to perched falcons. Flying is faster, but I would think swim-
ming is safer. However I never saw a Gyrfalcon strike at flying ducks in this situation
either.

116

RAPTOR RESEARCH

Vol. 14 No. 4

The most common method of hunting at Myvatn seemed to be the “sneak attack”
from a perch. The gyr watched from some advantageous (not necessarily very spec-
tacular) lookout, and then flew, dropping down almost to the ground and moving with
startling rapidity just over the ground or the scrub toward an unsuspecting, nonflying
prey. 1 saw this method used once in March against ptarmigan and again in August
against shorebirds, but it was most apparent during the display period of the cock
ptarmigan. A search of a busy moor often revealed a Gyrfalcon, perched motionless,
watching the activity of the noisy cocks around it. By June it seemed as if every other
ptarmigan display post had a few feathers or a wing from a previous occupant. Bengtson
(1971) reports similar observations and states that the most common hunting technique
was the snatching from the ground, or more rarely water, of an unsuspecting prey.

Both White and Weeden (1966) and Cade (1960) mention a high flight by Gyrfalcons,
which they connect with hunting behavior. Bengtson (1971) saw soaring frequently.- 1
observed soaring in several different situations. Two had to do with display. Soaring pre-
ceded mutual gliding at Seljadalur and followed an attack on an intruding gyr at Dim-
muborgir. On 13 June the female at Falkaklettur soared until almost out of eyesight
(about 350 m up) and then traced a great circle about the eyrie in what was apparently
either a signal to or a search for the male, which had not come with prey for the 8 hours
1 had been watching. She returned in about half an hour, overheated, without the male
and without prey. The Seljahjallagil pair often soared at 200-300 m when leaving the
gil for the lakeshore and vice versa, when returning with prey. It was undoubtedly an
easier way than direct flight to cross the 7-8 km of sandy waste that intervened. White
and Cade (1971) suggest that Gyrfalcons may go up to 10 miles from the nest to obtain
prey. The restricted location of available ducks, gulls, and shorebirds in midsummer at
Myvatn makes commutes of somewhat lesser distances necessary for several of the My-
vatn eyries. 1 saw adults at Seljahjallagil returning with prey from the direction of the
lake and leaving the lakeshore with prey in the direction of the eyrie.

Finally, the male at Dimmuborgir sometimes soared, but not so high, and then went
into a long glide when leaving the area. In short, 1 did not see soaring, or soaring and
gliding used by Gyrfalcons for hunting, but only for travelling and display.

Treatment of Prey

Finnur Gudmundsson (pers. comm.) suggested that one difference between the treat-
ment of prey by Gyrfalcons and ravens is that, while both species pluck their prey, only
Gyrfalcons pluck the primaries. Hagen (1952) reported that in 31 Gyrfalcon kills all had
had some primaries plucked. Of the wings of the approximately 250 Gyrfalcon kills that
I examined, only one had not had at least one primary plucked. The number of pri-
maries plucked varied from 1 or 2 to virtually all. Most of the carcasses I inspected were
from eyries with young, and casual observation indicates that such remains are handled
much more extensively than those killed and eaten by adults elsewhere. But carcasses of
Gyrfalcon kills from the prehatching period and from the early flying stage (when the
amount of handling seems to decrease) also had plucked primaries.

I noted three other characteristics of Gyrfalcon kills. In smaller-boned prey, such as
ptarmigan, the head is almost always eaten. It is apparently bitten off from the back.
The mandibles can often be found, sometimes with enough of the frontal skull attached
to determine the sex of the bird. Hagen (1952) reports not finding heads among the re-
mains, the implication being that they are discarded or eaten. Secondly, a length of in-
testine and sometimes the gizzard are removed and discarded. I found such lengths near

Winter 1980

W oodin— Gy rf alcons

117

kills “in the field” and at eyries after the young had fledged. Hagen (1952) reports that
the “intestines (gizzards)” tend to be eaten, but he may be simply saying that they were
missing from the kills. In April after snow thaw I found many mats of discarded in-
testines along the base of the Dalfjall ridge, with both bird mutes and fox scats next to
them. The mutes could have heen from either Gyrfalcons or ravens. The intestines ap-
peared to be all that remained of Gyrfalcon kills that had been scavenged by ravens and
foxes. The scavengers apparently were not interested in the intestines either. Finally, the
Gyrfalcon does a neat job. The breast is cleanly stripped of flesh, as may also be the legs
and wings. With smaller prey, the keel may have large bites taken out of it or be eaten
completely down. The raven’s work tends to be cruder in appearance.

Prey of the Gyrfalcon

In compiling prey remains (tables 2, 3, 4), I took Cade’s (1960) approach to numerical
estimation. I matched right and left wings by sex and species and then with sterna or

Table 2. Prey Remains Collected from the
Falkaklettur Eyrie in 1967.

6/2”

6/13”

7/3

7/9

7/11”

7/l/

Ptarmigan (Lagopus mutus)
Mallard {Anas pJatyrhynchos)
Gadwall {Anas strepera)

34"

6

4^

1

l5"

3-4

Wigeon {Anas penelope)
Pintail (Ana.s acuta)

3

1

1

Anas spp.

2

Tufted Duck {Aythya fuligula)
Scaup {Aythya marila)

2

1

1

1

Aythya spp.

Old Squaw {Clangula hyemalis)
Barrow’s Goldeneye
{Bucephala islandica)
Red-breasted Merganser

1

1

{Mergus senator)

Gommon Scoter {Melanitta nigra)
Duck spp,

2

4

1

Total ducks (%)
Black-headed Gull

0(0)

0(0)

9(16)

9 (35)

1(10)

3 (38)

{Larus ridihundus)

l’’

3"

F

Golden Plover {Charadrius

apricarius)

Whimbrel {Numenius phaeopus)

1

I**

Redwing {Turdus iliacus)

I**

Unknown

1

Total other than ptarmigan (%)

0(0)

0(0)

12 (21)

11 (42)

4 (40)

4(50)

Estimated date of hatching May 20-25.

“Remains in the eyrie and immediately about it not collected, or lost.

^12 old, 22 new.

33 old, 4 new, 8 uncertain,

,10 old, 5 new.

6 old.

j;2 juvenile, 1 of unknown age.

Eyrie deserted at least 2 days before. All the prey remains were fresh.

^Age unknown.

Juvenile.

118

RAPTOR RESEARCH

Vol. 14 No. 4

other body parts present. Backbones, while used as a rough check on the total numbers
of prey collected, were, because of the difficulties in identifying them, not associated
with the rest of a skeleton. It was often possible to check such skeletal reconstructions
by trying the fit of bones into corresponding sockets.

Ducks were difficult to identify. A. Gardarsson assisted me in their identification. Pri-
maries had usually been plucked entirely except for two or three; and we had to work
with what few feathers remained and the general size and shape of the skeleton. Unfor-
tunately, the soft sternal edges and keel, whose outlines are useful in separating the duck
species, were habitually bitten away. Feathers commonly left included one or more of
the following: upper and lower leading wing edges; scattered primaries and secondaries;
scapulars; coverts; or a tuft from the side of the breast.

The tables do not provide a reliable chronological estimate of prey brought to the
eyries because of the removal of remains from the nest vicinity by adults. Such removal
was rather irregular. At Dimmuborgir it became more frequent after hatching. Some

Table 3. Prey Remains Collected from the
Dimmuborgir Eyrie in 1967.

6/3

6/5

6/16

6/27

7/3

7/12f

Ptarmigan (Lagopus mutus)
Mallard {Anas platyrhynchos)
Gadwall {Anas strepera)

19

3

6

4

5

4

Wigeon {Anas penelope)
Pintail {Anas acuta)

2

9

3

3

Anas spp.

Tufted Duck {Aythya fuligula)
Scaup {Aythya marila)

1

2

Aythya spp.

Old Squaw {Clangula hyemalis)
Barrow’s Goldeneye

1

1

{Bucephala islandica)
Red-breasted Merganser

{Mergus senator)

Gommon Scoter {Melanitta nigra)
Duck spp.

3^

Total ducks (%)
Black-headed Gull

0(0)

0(0)

2 (25)

11 (73)

4 (44)

8 (67)

{Larus ridihundus)
Golden Plover {Charadrius

apricarius)

Whimbrel {Numenius phaeopus)
Redwing {Turdus iliacus)
Unknown

1

Total other than ptarmigan (%)

1(5)

1(5)

2(25)

11 (73)

4 (44)

8(67)

Date of hatching. May 25.

^The nest had been abandoned at least one day before.

^,One of the ducks was a duckling.

A small, blue, maggot-infested duck foot. The unknown on 3 June consisted of a matched radius and ulna. The foot appears to antedate this
collection, and the two remains may be from the same bird.

Winter 1980

W oodin— Gy rfalcons

119

remains were dropped within 100 m of the eyrie, others carried further off (see Weir
1967). The more distant remains were probably quickly scavenged by ravens or Arctic
foxes.

Collection problems at the Falkaklettur and Seljahjallagil eyries included the appear-
ance of old ptarmigan remains along with the new ones in my weekly or fortnightly
collections— apparently because 1 never found all the remains at any given time. The
aggressiveness of the females at these eyries made collection difficult. Both sites had
been used in the recent past, and the slopes beneath were speckled with bits of remains.
Remains of smaller prey get broken badly by the young if they remain in the eyrie over
any period of time. They dry out rapidly and blow about; some undoubtedly get lost.
Old remains may get dug out of the mud of the eyrie shelf. Since I found it difficult to
be absolutely sure about what was old and what new, I composed the tables according
to what was picked up with the “old” and “new” designations in footnotes.

With these qualifications, the data in the tables suggest that there was a shift in the
prey taken, from ptarmigan to other species, that occurred from the second week of
June onward. Prior to 16 June the only remains I found at Dimmuborgir, with two ex-
ceptions, were of ptarmigan. On 16 June I found remains of two Widgeon (Anas pene-
lope) along with six ptarmigan, and on 27 June, nine Widgeon, two unidentified ducks,
and four ptarmigan. At Falkaklettur I found the first remains other than ptarmigan on 3
July. Thus at Dimmuborgir the shift began between 5 and 16 June and at Falkaklettur
between 13 June and 3 July. The Falkaklettur eyrie was situated in an area where prey
other than ptarmigan was either scarce or a considerable distance away.

The shift in prey can probably be correlated with changes in the behavior of the cock
ptarmigan. When I arrived at Myvatn in early March, the chief prey of the Gyrfalcons
appeared to be ptarmigan. At the same time, ducks were present in some numbers. A
count on 3 March along 4 km of the lake (including most of the lake that remains open
during winter) gave 170 Barrow’s Goldeneye (117 males, 53 females), about 100 Goosan-
ders (Mergus merganser) (sexes equally divided), about 45 Mallards (Anas platyrhynchos)
(30% females), along with 37 Whooper Swans (Cygnus cygnus). The ducks did not ap-
pear to be taken in any numbers. Migratory waterfowl begin arriving in mid-April. By
May they are present in force.

About the middle of April ptarmigan cocks begin to set up territories. For the next 2
months predation seemed to fall heavily on them. The cocks keep their white plumage
and preoccupation with territorial defense into early June. Thus they remain vulnerable
to Gyrfalcon predation through the beginning of that month. Signs of Gyrfalcon pre-
dation on ptarmigan cocks in the form of remains on (reoccupied or unoccupied) display
posts are common during the display period.

In June, when the ptarmigan egg clutches are complete, the cocks acquire summer
plumage and become much less territorial and more skulking in behavior. There is still
some erratic display, especially at twilight, and since Gyrfalcons hunt at night in sum-
mer, the cocks remain still somewhat vulnerable. In the Myvatn area this midnight dis-
play activity continued into July.

For the Gyrfalcons, the change in the behavior of the cocks comes at a pivotal time—
a week or two after the young have hatched and need a large and regular supply of
food. The male, which ordinarily does all the hunting during the first part of the nest-
ling stage, must now hunt for the equivalent of three adults or more. Thus he has a pow-
erful stimulus to break whatever “fix” he has on ptarmigan and to turn to other species.

120

RAPTOR RESEARCH

Vol. 14 No. 4

Table 4. Prey Remains Collected from the
Seljahjallagil Eyrie in 1967.

6/30

7/7

7/13

7/19

Ptarmigan {Lagopus mutus)

11

4

17"

17^

Mallard {Anas platyrhynchos)
Gadwall (Anas strepera)

1

3

1

Wigeon (Anas penelope)

3

2

4

2

Pintail (Anas acuta)
Anas spp.

1

6

1

Tufted Duck (Aythya fuligula)

7

1

3

Scaup (Aythya marila)

4

3

1

2

Aythya spp.

5

2

2

Old Squaw (Clangula hyemalis)
Barrow’s Goldeneye

2

1

1

(Bucephala islandica)
Red-breasted Merganser

2

(Mergus senator)

Common Scoter (Melanitta nigra)

1

1

Duck spp.

7

11

7

f

Total ducks (%)
Black-headed Gull

29 (73)

22 (81)

24 (53)

13 (34)

(Lams ridihundus)

1

4^

Golden Plover (Charadrius
apricarius)

Whimbrel (Numenius phaeopus)
Redwing (Turdus iliacus)
Unknown

Total other than ptarmigan (%)

29 (73)

23 (85)

28 (62)

21 (55)

Estimated date of hatching May 20-25.

old, 7 new.

15 old, 2 new.
juvenile, 3 unknown age.
^Age unknown.

Duckling of diving duck.

The completeness of the shift probably depends on the availability of these species to
individual Gyrfalcons. Since habit enters in, and chance falcon-ptarmigan encounters
occur, one would not expect a complete shift in most cases. As mentioned above, Gud-
mundsson and Gardarsson found that predation by Gyrfalcons on the nesting ptarmigan
of Hrisey virtually ceases in early June. Hrisey is about 4 km from the nearest point on
the mainland and likely at least twice that from the eyrie from which they surmised the
Gyrfalcons are coming. In such a situation, where Gyrfalcons come from a considerable
distance to hunt an island almost exclusively for ptarmigan, and where “reservoir spe-
cies” exist elsewhere, the shift might appear much more complete. An investigator col-
lecting remains from the eyrie of those same Gyrfalcons might continue finding ptarmi-
gan that were picked up closer to the eyrie.

Winter 1980

W oodin— Gyrfalcons

121

A corollary of the shift in prey seems to be that the presence of one or more “reser-
voir species” is helpful for the successful raising of young by Gyrfalcons whose primary
prey is ptarmigan, especially in years of marginal ptarmigan populations, where perhaps
ptarmigan are abundant enough to induce the Gyrfalcons to breed, but not abundant
enough to ensure survival of the young. Cade (1960) and White and Cade (1971) de-
scribe situations somewhat like this along the Colville River in Alaska. The Colville
Gyrfalcons prey almost exclusively on ptarmigan, and their breeding success, or whether
they will breed at all, fluctuates with the ptarmigan population. In 1959 Cade (1960)
observed a shift to rodents and rodent-eating birds about the middle of June. He ex-
plained the shift by the concurrent departure of a high late-winter ptarmigan popu-
lation, which had induced a record number of Gyrfalcons to breed, and the snow melt-
off that exposed a peak rodent population. The rodent population attracted many non-
breeding, rodent-eating birds that were highly vulnerable to Gyrfalcon predation.
Cade’s explanation is rather speculative, and it is difficult to assess whether the shift in
prey was motivated by a special situation or whether pressure exists for it annually.

Hagen (1952) describes an apparently marginal breeding situation for ptarmigan-
dependent gyrs in the Norwegian mountains, in which successful breeding in a certain
valley coincided with peak rodent years. Rodents were not important in the diet of the
Norwegian Gyrfalcons. Hagen speculates that the coincidence has three causes: (1) Less
pressure from other predators makes Willow Ptarmigan {Lagopus lagopus) live more
openly in peak rodent years (an observed fact); (2) competition between carnivores is
reduced in high microtine-rodent years; and (3) the two Lagopus species that form the
bulk of the Gyrfalcons’ prey tend to fluctuate with the microtine-rodent cycles and are
more abundant in years of high microtine population. Thus, in a situation where a satis-
factory reservoir species for the gyrs apparently does not exist, other factors tend to cre-
ate the same effect in certain years.

Bengtson (1971) reports data concerning a prey shift in Myvatn Gyrfalcons, in the
form of prey being transported by flying Gyrfalcons. For ducks being transported in the
months May through August, the numbers are 15, 10, 20, 20; for Rock Ptarmigan in the
same months, the numbers are 9, 8, 3, 1. Thus Bengtson observed an increase in ducks
being carried in July and August, and a decrease in Rock Ptarmigan during those
months. Bengtson’s studies focused on the waterfowl population, and there is no way of
knowing how random his sample was. It may be biased toward ducks. He certainly re-
cords relatively more ducks being taken in May and June than I observed. However, this
situation may vary from eyrie to eyrie and year to year. For instance, the Vindbelgjarf-
jall eyrie, unproductive in 1967, is located amidst some of the best waterfowl habitat at
Myvatn. Parts of their hunting grounds for ptarmigan are also good waterfowl habitat.
It would be surprising if this pair did not take waterfowl in substantial numbers early in
the season.

My data suggest the tendency toward specialization at the three eyries on Widgeon,
Tufted Duck (Aythya fuligula), and Scaup (Aythya marila). Much has been written
about the Gyrfalcon’s tendency to develop a “fix” on prey, and these data perhaps sup-
port the notion. There is some question in my mind about whether such “fixes” are the
result of prey behavior or prey presence. The three ducks in question are also the three
most common species at Myvatn, according to Bengtson (1971). Even more to the point,
as I have tried to show, a Gyrfalcon hunting ptarmigan in May faces quite a different
situation from one hunting them in March.

122

RAPTOR RESEARCH

Vol. 14 No. 4

Distribution of Nests

If one ignores the eyrie at Seljadalur, all the eyries to the east of the lake were spaced
between 9 and 11 km apart. This distribution suggested that perhaps the gyrs at Seljada-
lur and Dalfjall failed to breed because their potential nests were “psychologically” too
close together. If the gyrs at Holkotsgil were not the same as those at Vindbelgjarfjall,
this hypothesis would also explain the nonbreeding at Vindbelgjarfjall. However, I was
not able to confirm the status of the Holkotsgil gyrs. At any rate, this hypothesis did not
explain why the Gaesadalur birds bred.

Seljadalur is about 5.5 km from both Dalfjall and Gaesadalur. If this distance were
below the minimum territorial limit for Icelandic Gyrfalcons, one would expect to see
at least some agonistic behavior, and I did not. In Alaska, Gyrfalcons have nested as
close as 3.2 km, though the average is about 17 km (White & Cade 1971). In western
Greenland the mean minimum distance between 7 sites was 7.8 km (Burnham 1975).
Ernest Vesey found three cases of pairs of Gyrfalcons nesting within 4 or 5 km of each
other in the western fjords of Iceland in 1936. All these sets of pairs laid eggs, one of the
sets of pairs raised young, and at least one pair in the other two sets raised young. The
fact that none of Vesey ’s nests were closer than 4 or 5 km, combined with (a) my finding
of pairs residing at minimum distances of about 5.5 km, plus (b) the discovery of what
appeared to be alternate sites or areas within 3 or fewer km of currently occupied sites,
leads me to conclude that the minimum “psychological” distance between nesting pairs
of Gyrfalcons in Iceland is between 3 and 5 km.

The most likely explanation for the nonbreeding at Myvatn in 1967 is probably the
classical one. Ptarmigan populations over the whole of Iceland follow a well-defined
ten-year population cycle (Gudmundsson I960). Bengtson (1971) reported densities of
breeding ptarmigan for the years I96I-I966 increasing from 1.7 to 7.4 per km^ at My-
vatn. According to A. Gardarsson (pers. comm.) and Bengtson (1971), 1966 was a peak
ptarmigan year. Presumably the population of surviving Gyrfalcons in the spring of
1967 was at a peak, and the occupation of potential breeding sites at Myvatn was also at
a peak. (This is one of the considerations that led me to define unoccupied, previously
used nests 3 km or less from occupied nests as “alternative eyrie areas.” If they were not
“too close” to occupied nests, some should be occupied in a peak Gyrfalcon year.) How-
ever, the ptarmigan population had fallen in the spring of 1967 from the spring of 1966.
Thus a relative lack of prey was probably the primary stress causing nonbreeding by
Gyrfalcons at Myvatn in 1967. The tendency of the closer resident pairs, with (one as-
sumes) smaller home ranges, not to breed would appear compatible with this hypothesis.
At the same time the pair at Seljadalur had the additional stress of competing with a
pair of ravens, and the pair at Vindbelgjarfjall may have been disturbed by the presence
of immatures.

My interpretation of eyrie areas at Myvatn is rather speculative. Observation over an
entire lO-year population cycle of the ptarmigan would be the only way of clarifying
the situation. The status of the Seljadalur eyrie especially is problematic. Only observa-
tion over a period of years would determine whether it should be considered an inde-
pendent area or an alternate to Gaesadalur, I would attach Seljadalur to Gaesadalur
rather than to Dalfjall because the Dalfjall ridge eontained several alternate sites while I
only found one each in Gaesadalur and Seljadalur.

Winter 1980

W oodin— Gyrfalcons

123

Literature Cited

Beebe, F. L. 1960. The marine peregrines of the northwest Pacific coast. Condor
62(3): 145-189.

Bengtson, S.-A. 1971. Hunting methods and choice of prey of Gyrfalcons {Falco rustic-
olus) at Myvatn in northeast Iceland. Ihis 113:468-476.

Brown, L., and Amadon, D. 1968. Eagles, hawks and falcons of the world, vols. 1, 2.
New York: McGraw-Hill.

Burnham, W. A. 1975. Breeding biology and ecology of the Peregrine Falcon {Falco per-
egrinus) in West Greenland. Master’s thesis, Brigham Young University, Provo,
Utah.

Cade, T. J. 1960. Ecology of the peregrine and Gyrfalcon populations in Alaska. Univ.
Calif. Publ. Zool 63:151-290.

Cade, T. J., and Weaver, J. D. 1976. Gyrfalcon-peregrine hybrids produced by artificial
insemination./. N. Amer. Falconers’ Assoc. 15:42-47.

Cramp, S., and K. E. L. Simmons (eds.). 1980. The birds of the western Palearctic. Ox-
ford University Press, vol. 2.

Dementiew, G. P. 1960. Der Gerfalke. Franckh’sche Verlagshandlung— Kosmos Verlag,
Stuttgart.

Gudmundsson, F. 1960. Some reflections on Ptarmigan cycles in Iceland. Proc. Int. Orn.
Congr. 12:259-265.

Hagen, Y. 1952. The Gyr-falcon in Dovre, Norway. Skr. Norske Vidensk Akad. I. Math.-
Nat. Kl. No. 4, 1952:1-37.

Jenkins, M. A. 1974. Behavior of the Gyrfalcon {Falco rusticolus) from hatching to fledg-
ing: a time-lapse photographic study. Master’s thesis. Brigham Young University,
Provo, Utah. 83pp.

Lewis, E. (pseudonym of E. Vesey). 1936. In search of the Gyrfalcon. London.

Platt, J. B. 1976. Gyrfalcon nest site selection and winter activity in the western Cana-
dian arctic. Can. Field-Naturalist 90(3):338-345.

Snyder, N. E. R., and J. W. Wiley. 1976. Sexual size dimorphism in Hawks and Owls of
North America. A.O.U. Monograph #20.

Storer, R. W. 1966. Sexual dimorphism and food habits in three North American accipi-
ters. Auk 83:423-436.

Sutton, G. M. 1961. Iceland summer: adventures of a bird painter. University of Okla-
homa Press, Norman.

Wayre, P., and Jolly, G. E. 1958. Notes on the breeding of the Iceland Gyr-falcon. Brit.
Birds 51:285-290.

Weir, D. N. 1967. Possible source of error in raptor food analysis. Bird Study 14:194.

White, C. M., and Cade, C. J. 1971. Cliff-nesting raptors and ravens along the Colville
River in arctic Alaska. Living Bird 10:107-150.

White, C. M., and Weeden, R. B. 1966. Hunting methods of Gyrfalcons and behavior of
their prey (Ptarmigan). Condor 68(5):517-519.

124

RAPTOR RESEARCH

Vol. 14 No. 4

Figure 3. View from the lip of Dimmuborgir into the depression. The photo does not give an adequate idea of
the depth or the extensiveness of Dimmuborgir. In the distance some of the hills that form the eastern bound-
ary of the Myvatn basin. In the foreground low bushes of birch {Betula pubescens). May 1967.

Figure 4. View of Hrossaborg from the road across the Burfellshraun. The Gyrfalcon eyrie is on the opposite
side. Note the sparsely vegetated “.sandy waste.” In the distance are the mountains of the Central Highlands
of Iceland. June 1967,

Winter 1980

Abstracts

125

ABSTRACTS OF THESES AND DISSERTATIONS

RELEASE OF CAPTIVE-PRODUCED PEREGRINE FALCONS IN THE
EASTERN UNITED STATES, 1975-1979

Two hundred and four captive-produced Peregrine Falcons (Falco peregrinus) were
released by hacking at 21 locations in the eastern United States during 1975-1979. Sev-
enty-two percent (146) of the hacked falcons survived to independence and dispersed
normally from the release sites. Hacking success was significantly higher at artificial
(tower) sites than at natural (cliff) sites. Higher mortality during hacking at cliffs was
due primarily to a higher incidence of Great Horned Owl {Bubo virginianus) predation.
The falcons have not been migrating, and first-year survival appears comparable to the
first-year survivorship of wild peregrines. Band recovery data suggest that peregrines
released by hacking are no more vulnerable to shooting than wild peregrines.

The highest incidence of birds returning to release sites has been in coastal New Jer-
sey. Some of the factors contributing to regional differences in return rates are dis-
cussed. Prey availability appears to be one of the major determinants of the suitability
of artificial sites for eventual occupancy by breeding pairs. Many birds, including prog-
eny of tundrius peregrines, have shown signs of incipient reproductive behavior upon
returning to release sites. Three groups of young placed for hacking were adopted by
parentally motivated single adults. The first known pairing of released falcons occurred
in 1978. Three pairs were known in 1979, all at tower sites in coastal New Jersey. One
of these, consisting of an adult male and subadult female, produced fertile eggs which
were damaged late in incubation during aggressive encounters with Fish Crows (Corvus
ossifragus). An unpaired adult female laid eggs on a skyscraper in Baltimore, Maryland,
in 1979. Analysis of the eggs from both females revealed shell thicknesses within the
range of hatchability and low levels of pesticide residues.

The population of released peregrines is estimated at approximately 50 subadults and
adults in the spring of 1980. A computer simulation describes the growth of the popu-
lation up through 1990.

Barclay, John H. 1980. Release of captive-produced Peregrine Falcons in the eastern
United States, 1975-1979. M.S. thesis, Michigan Technological University, Hough-
ton, Michigan 49931.

LARGE RAPTOR ELECTROCUTION AND POWERPOLE UTILIZATION:
A STUDY IN SIX WESTERN STATES

To determine the factors influencing the majority of raptor electrocutions in the
West, data from 24 five-mile sections of powerline were collected in six states, Idaho,
Oregon, Nevada, Utah, New Mexico and Wyoming. Soil and vegetation types, topo-
graphic relief, weather patterns, and prey base were all considered to isolate the ecolog-
ical types where the problem most often occurred. Human disturbance both active and
passive was considered, and an attempt was made to eliminate bias due to shooting.
Raptor age was determined, when possible, to assess the impacts upon breeding and sub-

126

RAPTOR RESEARCH

Vol. 14 No. 4

adult populations. Configuration and power output of the poles were considered to de-
termine the most hazardous constructions. These data are necessary to allow power
companies and state and federal management agencies to determine modification needs
and the most practical methods for eliminating raptor electrocutions.

It is concluded that subadult age classes are more affected than adults because of in-
experience in flight and different hunting methods. Most eagles were electrocuted in
winter when “still” hunting was most used and when precipitation in the form of snow
caused greater feather wetting. More eagles were electrocuted in areas where cottontail
rabbits were present than where only jackrabbits occurred, and this difference is related
to hunting methods. While pole configuration, related to power output, is the most sig-
nificant factor, most newly constructed powerlines are modified to reduce or eliminate
this problem.

Benson, Patrick C. 1981. Large raptor electrocution and powerpole utilization; a study
in six western states. Ph.D. dissertation, Brigham Young University, Provo, Utah
84602.

HARRIER RADIO-TAGGING TECHNIQUES AND LOCAL AND
MIGRATORY MOVEMENTS OF RADIO-TAGGED JUVENILE HAR-
RIERS

The purpose of this study was to determine postfledging movements of juvenile
Northern Harriers (Circus cyaneus hudsonius) hatched on the Buena Vista Marsh in cen-
tral Wisconsin. This determination necessitated radio-tagging of both adult and nestling
harriers. Breeding harriers have adapted poorly to backpack harnesses in the past. I used
three radio-packages: double-loop backpack, crossed-loop backpack, and tail-feather
mount. The double-loop backpack proved unsuitable on two of three adults tagged in
1976; one female died of starvation 10 days after being tagged, and another partially
deserted her young. A male accepted the double-loop backpack quickly. The crossed-
loop backpack was used successfully on seven fledglings, two in 1976 and five in 1977.
The tail-feather mount was readily accepted by eight of nine breeding adults in 1977.
One female removed her radio-tagged feather almost immediately after attachment but
then resumed normal behavior.

I followed the local movements of seven radio-tagged juveniles from three nests in
1976 and 1977 and the early migratory movements of three of these juveniles in 1977.
All seven remained within 0.9 mi (1.4 km) of their nests for about 3 weeks after their
first flights. They did little or no hunting during this period. Five of the seven left the
study area about 21 days after fledging. One juvenile was killed near his nest by a Great
Horned Owl (Bubo virginianus) 33 days after fledging, and the last one left the study
area 52 days after fledging.

Of the six juveniles that left the study area, four were known to have left alone, rather
than with parents or siblings. Three were located during migration. Their migratory
movements were interrupted by the establishment of temporary home ranges which
were used for 2-3 weeks. One juvenile was located 44 mi (71 km) southeast of her nest.
Another was monitored in two temporary home ranges, one 53 mi (85 km) east-south-
east and another 106 mi (171 km) southeast of his nest. A third juvenile was tracked

Winter 1980

Book Reviews

127

continuously until she was in a temporary home range 102 mi (164 km) southeast of her
nest. All known locations of the migrating juveniles were in the southeast quarter of
Wisconsin. Case histories of the movements of these three juveniles are presented in de-
tail.

Beske, Alan E. 1978. Harrier radio-tagging techniques and local and migratory move-
ments of radio-tagged juvenile Harriers. M.S. thesis, University of Wisconsin, Ste-
vens Point, Wisconsin. 47 pp.

Present address: P.O. Box 165

Waupun, Wisconsin 53963

BOOK REVIEWS

Birds of Prey of the World. Friedhelm Weick. 1980. Verlag Paul Parey,
Hamburg and Berlin, 1,144 color figures, 160 line drawings. $48.00. 159 pp.

Weick, inspired by Peter Scott’s colored key to the world’s waterfowl format, has pat-
terned his book after it. It will likely have a restricted appeal to the general public but
should gain wide use among professionals, graduate students, hawk watchers, museum
types, and the like. It is not the coffee-table brand of artwork, but then it was not in-
tended to be. There are two sections, each printed in both English and German. The
first section is 60 pages long. This section contains keys to groups by color, size, and
other field marks. The best drawings, together with descriptions, are here, and each
genus is represented. Good as the illustrations are, however, I found part of this section
of little practical value. How does one judge a “large” from a “rather large” bird? In my
opinion, Peregrine Falcons have “plumage contrasting, dark and light” not “plumage
brightly colored” as they are listed.

The technician and falconophile should love the second section: 40 color plates of
uniformly depicted side-view figures. Some 1,144 figures are represented. Individual
plates display as few as 12 to as many as 52 figures; some appear quite crowded. Imma-
tures for all species are shown, except for three apparently with undescribed plumages,
the Madagascar Serpent Eagle from Madagascar, New Britain Gray-headed Goshawk
from New Britain Islands, and White-browed Hawk from central South America. Of the
670 subspecies described, 574 are illustrated. There are some evident errors in the accu-
racy of the art. Several examples follow: immature plumages of the Black and Wedge-
tailed Eagles do not show the evident contrasting brown-cinnamon colors. Eye color of
adult and juvenal Bald Eagles are shown the same. Adult male and female plumages of
the North American Rough-legged Hawk (B. 1. sancti-johannis) are shown as being the
same. The tail bars of the Pacific Northwest Merlin (F. c. suckleyi) are shown to be as
light as they are on the nominate form. Gheeks of the adult Black Falcon are shown as
being pale rather than dark. Though the book has shortcomings, they are but minor, and
on balance Weick deserves hearty commendation for a job nicely executed with a taste-
ful layout.

Glayton M. White

128

RAPTOR RESEARCH

Vol. 14 No. 4

Der Sakerfalke, Falco cherrug. Wolfgang Baumgart. Neue Brehm Bucherei
no. 514. A. Ziemsen, Wittenberg-Lutherstadt, DDR, 1980. 160 pp, 74 figs,
(chiefly photos), 1 color pi., 2d ed. (1st 1978).

Of the 500 odd titles in the Neue Brehm Bucherei series, this is, if I have succeeded in
obtaining them all, the 20th (not counting revised editions) devoted to raptors— 13 to
diurnal birds of prey, 6 to owls, and 1 to pellets and prey remains. More than half the
number, like the present one, are single species monographs, written by specialists, or
concern a small group of allied species such as the Golden, Verreaux’s, and Wedge-
tailed Eagles. Many of the species occur in America; others have close relatives. Such is
the Saker Falcon, a close relative of our Prairie Falcon and Gyrfalcon, though perhaps
less confined to treeless areas, for it often uses old tree-nests of Ravens and the like.
Copiously illustrated and well documented, though somewhat cheaply produced, the
relevant volumes in this series should be acquired by libraries purporting to cover pre-
dation and birds of prey. The color plate was first published by Otto Klienschmidt and
shows the geographic races that Kleinschmidt considered belonging to the Gyrfalcon
group. Obtaining material from East Germany is not always easy; the present volume
was purchased from Universitaire Bockhandel, 1 Damsterdiep, Groningen, Holland for
$15.25. It can be obtained through Buteo Books.

Dean Amadon

The Merlins of the Welsh Marehes. D. A. Orton. 1980. 168 pp., 8 photos.
David and Charles, North Pomfret, Vt. 05053.

The author, a retired businessman, spent numerous days over four years watching and
meticulously recording the behavior of nesting Merlins on the moorlands of the Welsh
Marches (borderlands). The reader of this charmingly written account, regardless of ex-
perience, will learn much of what is normal, what exceptional, in the activities of this
dynamic little falcon.

Dean Amadon

THE RAPTOR RESEARCH FOUNDATION, INC.
OFFICERS

President Dr. Richard R. Olendorff, Division of Resources (C-932), 2800

Cottage Way, Sacramento, California 95825

Vice-President Dr. Joseph R. Murphy, Department of Zoology, 167 WIDE,
Brigham Young University, Provo, Utah 84602

Secretary Dr. Jeffrey L. Lincer, P.O. Box 8, Sarasota, Florida 33578

Treasurer Dr. Gary E. Duke, Department of Veterinary Biology, College of
Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108

Address all matters dealing with membership status, dues, publication sales, or
other financial transactions to the Treasurer. See inside front cover.

Send changes of address to the Treasurer.

Address all general inquiries to the Secretary.

See inside front cover for suggestions to contributors of manuscripts for Raptor
Research, Raptor Research Reports, and special Raptor Research Founda-
tion publications.

BOARD OF DIRECTORS

Eastern Dr. Mark R. Fuller, Migratory Bird Lab., U.S.F.W.S., Patuxent Re-
search Center, Laurel, Maryland 20811

Central Dr. Patrick Redig, Department of Veterinary Biology, College of Vet-
erinary Medicine, University of Minnesota, St. Paul, MN 55101

Pacific and Mountain Dr. Joseph R. Murphy, Department of Zoology, 167
WIDE, Brigham Young University, Provo, Utah 84602

Canadian Eastern Dr. David Bird, Macdonald Raptor Research Center, Mac-
donald College, Quebec, H9X ICO, Canada

Western Dr. R. Wayne Nelson, 25 Montcalm Ave., Camrose, Alberta T4V
2K9, Canada

At Large Dr. Richard R. Olendorff (address above)

At Large Dr. Stanley Temple, Department of Wildlife Ecology, Russell Labora-
tory, University of Wisconsin, Madison, Wisconsin 53706

At Large Dr. Thomas Dunstan, Biology Dept., Western Illinois University, Ma-
comb, Illinois 61455